Heat butter in a large frying pan. Add the onion and carrot; cook, stirring, for about 5 minutes or until onion softens. Combine the onion mixture, tomato sauce, parsley, sausage mince, beef mince, breadcrumbs, salt and pepper in a large bowl; mix well.

Place a sheet of pastry on a board, cut in half. Place one sixth of the mince mixture along the centre of the pastry. Roll pastry to enclose the mince mixture, cut into 3 pieces. Repeat with remaining pastry and mince mixture. Place sausage rolls on prepared trays. Brush with milk.

Bake, uncovered, in a moderately hot oven for about 15 minutes or until browned lightly.